It is generally known that electrophotographic printers utilize toner to generate text and/or images on a print medium, such as, paper. In this regard, a toner cartridge is typically employed to store the toner. In the event the toner cartridge runs out of toner in the middle of a print job, paper and time may be wasted and users may become frustrated. Thus, to insure sufficient quantities of toner for a print job, sensors are often utilized to measure the toner level. However, sensors are expensive. In this regard, methods of toner estimation may be employed.
Previous inventions have disclosed methods of estimating toner usage for a print job. Typically, the toner usage is estimated for each print job. If the estimate indicates that insufficient toner is remaining in the cartridge, a user may be notified. For example, U.S. Pat. No. 5,802,420 discloses a method of predicting toner usage based upon printing history. For example, if a certain amount of toner was used to print the last 10 pages, the next 10 pages is estimated to use that same amount. U.S. Pat. No. 5,937,255 discloses a method of estimating toner usage based upon a pixel count. For example, if “T” amount of toner is used to generate one pixel, then 100 pixels is estimated to use 100×T amount of toner.
However, different pixels may not utilize the same amount of toner. For example, in the assignee's HP Monochrome and Color LaserJet™, a laser light source is modulated as it scans across the surface of an optical photoreceptor (“OPR”). To create a pixel, the laser light source may be modulated (or pulsed) to illuminate a desired pixel location. However, the pixel does not represent a fixed quantity of toner. For each pulse, the length of time (or duration) the laser is on as it scans across the OPR correlates to the width of the pulse on the OPR surface. The width and number of pulses used to create a pixel may vary from one pixel to another pixel. For example, to produce certain fine details, it may be advantageous to produce relatively narrow pixels. Thus, the duration of the pulse used to create the relatively narrow pixel may be correspondingly short. Conversely, relatively wider pulses may be used to produce a substantially solid line across the page.
Moreover, even for a given sized pixel, the amount of toner used may vary from pixel to pixel. For example, the number of pulses used to create a pixel may differ from pixel to another. A first pixel may be produced with a single pulse. A second pixel may be produced with more than one pulses. However, the first and second pixel may be substantially the same size despite using varying amount of toner based on the number of pulses.